.100"?! I think you'd get zero compression right after the pitons hit all the valves. Just to clean up the head before I installed it, it was milled .005". My engine builder tried to talk me into milling it to .050". I think .100 is way too much.
if you get the omniman video steve shows quite graphically you how over milling can cause the valves to hit and catch each other on a cam that has a high ramp rate.
the service mill recommended by Honda is 5 thou x 2 mills max. to clean the head and freshen it up for a flat surface to accept a new HG.
20 thou is considered safe with a stock HG.
I don't recommend 1 layer HG's even if you use copper spray. They just fail over time.
If you're trying to get more CR, try the flat faced intake valves by sk2 with stock diameters (don't oversize) instead of the 1 layer HG if you aren't willing to do it right using a bigger piston dome.
Then what is the max you can mill using a oem HG, on a very tight buget. I'm going to do the timing belt and HG at one time(along with all the other stuff that goes along with both projects) i.e water pump, gaskets, drivebelts.
if you look at the "compression ratio explained" article here (Performance, Enginei section), at the bottom of the article is a list of aftermarket 2 layer HG's.
I provided the thicknesses of those HG's and how many points of compression you increase.
from that you can deduce how much milling increases the CR.
on avg. 11-12 thou mill advances the cam timing by 1-2 degrees on the Bseries heads, depending on the chamber volume (GSR smallest and the LS the largest chamber volume: the larger the chamber volume, the less of an increase on static CR that you end up with for the same amount of milling).
the piston to head clearance for stock rods (you can run a little tighter with forged steel rods) and piston to valve clearance are 0.045 in. (45 thou). remember to include that once you milled.
for the most part 20 thou is considered "safe" if you're trying to slightly increase CR on your LS by 0.2-0.3.
the more you mill , the more you run the risk of weakening the head and also increasing the chance of HG failure.
people have gone as high as 35-40 thou but I don't recommend that high for reliability reasons and the effect on piston to head and piston to valve.
on the bigger aftermarket cams that have very steep ramps, milling the head brings the head closer to the deck and increases the chance of the valve hooking. omniman explains it and shows this to you in the omniman video. so that's another reason not to go too high on the milling.
The service mills to clean the head deck and ensure they're flat to accept a new HG and seal properly as recommended by Honda is 5 thou and they allow you to do that 2 times on a head and it won't significantly affect CR or cam timing according to them.
I always recommend to people to go with a 2 layer HG (not a 1 layer) instead of milling since a HG can be changed and bring you back to more clearance but milling is permanent.
have you considered that or the flat stock diameter intake valves that raise CR ?